How the electrochemical reversibility of a battery-type material affects the charge balance and performances of asymmetric supercapacitors

The charges stored within the pseudocapacitive materials are strongly affected by the charge-discharge rate because of their electrochemical reversibility, especially when employing a battery-type material in the asymmetric design. As a result, the charges stored in the positive and negative electrodes in asymmetric supercapacitors (ASCs) are usually not well balanced because of the wide-rate operation of ASCs. This work demonstrates how to construct an ASC with one electrode material of the battery type through the charge balance consideration using the nickel hydroxide//activated carbon (Ni(OH)2//AC) system as an example. Due to the fact that the electrochemical reversibility of Ni(OH)2 is worse than that of AC, the influences of the current density (at 0.5 and 80 A g−1) in evaluating the charge capacity of Ni(OH)2 on the cell capacitance, power ability, and stability of the ASC are investigated. The above parameters of this ASC are evaluated by cyclic voltammetric, constant current charge-discharge, and electrochemical impedance spectroscopic analyses. The proposed charge capacity has been demonstrated to be an important factor for determining the specific energy, power ability, and stability of ASCs. A general strategy for achieving the optimal performances of an ASC with one battery-type electrode is proposed in this work.